This invention relates to eliminating or substantially reducing the explosion hazard presented by mixtures containing nitrogen trifluoride and, in some of its more specific aspects, to reducing the explosion hazard in systems for producing, and handling nitrogen trifluoride. The invention further relates to electrolytic cells and to methods and systems in general which are especially useful for producing and handling gas mixtures containing nitrogen trifluoride.
In mixtures containing nitrogen trifluoride, e.g. gaseous or liquid mixtures such as the mixtures in systems for producing and handling nitrogen trifluoride, problems of explosions resulting from reactions between the nitrogen trifluoride and one or more of the components other than nitrogen trifluoride are presented. For example, in the production of nitrogen trifluoride by the electrolysis of a molten salt of hydrogen fluoride and ammonia, hydrogen is evolved along with nitrogen trifluoride and explosions often occur as a result of reaction between the hydrogen and nitrogen trifluoride. Problems of explosions are also presented in systems for the separation of nitrogen trifluoride from gaseous mixtures containing nitrogen trifluoride and components other than nitrogen trifluoride and in systems for carrying out reactions involving nitrogen trifluoride. Such explosions are dangerous to personnel, costly and result in production losses. Accordingly, the prevention of such explosions is of great importance.
U.S. Pat. No. 3,235,474, discloses a method to prevent explosion hazards in mixtures, e.g. gaseous or liquid mixtures containing nitrogen trifluoride by keeping the concentration of the nitrogen trifluoride in the mixture outside the range of 9.4 to 95 mol percent by diluting the mixture with diluents, hydrogen or nitrogen trifluoride. Suitable diluents are nitrogen, argon, helium and hydrogen. And U.S. Pat. No. 3,235,474 states that accordingly, a preferred method embodying the principles of this invention for eliminating or substantially reducing explosion hazards in mixtures containing nitrogen trifluoride and hydrogen comprises diluting the mixture sufficiently to maintain either the concentration of the nitrogen trifluoride at less than 9.4 mol percent or the concentration of the hydrogen at less than 5 mol percent.
Related references include JP2000104186A; JP2896196B2; U.S. Pat. No. 5,084,156; U.S. Pat. No. 5,085,752; U.S. Pat. No. 5,366,606; U.S. Pat. No. 5,779,866; US2004/0099537; EP1283280A1 and US20070215460A1. Some of these references disclose physical barriers or other physical aspects of the cell to prevent hydrogen from migrating from the cathode to the anode side of the cell. All of the references just listed and U.S. Pat. No. 3,235,474 are incorporated in their entireties herein by reference.
There still remains a need in the art for a method, electrolytic cell and system designs that reduce the explosion hazard presented by mixtures containing nitrogen trifluoride and hydrogen, particularly in the anode product gas.